The present disclosure relates generally to fiber optic cables, and more specifically to strength member systems of fiber optic cables.
Fiber optic cables typically include strength members, such as glass-reinforced plastic rods that bear stresses experienced by the cables, so as to reduce the transfer of loading to optical fibers carried by the cables. Some loose tube cables include a central guide about which buffer tubes containing optical fibers are stranded (e.g., helically wound). The central guide may include a strength member core with an overcoat or “up-jacket” of additional material that increases the diameter of the central guide so that the buffer tubes have a desired lay length for stranding.
Traditionally, physical bonding and tightness of the overcoat around the strength member core blocks water from penetrating and traveling through the cable between the strength member and the overcoat. Achieving the bond typically relies upon tight extrusion process controls, and in cases of thicker overcoats also may rely upon two or more separate passes down an extrusion line to maintain water-penetration integrity, due to shrinkage of the overcoat material (e.g., up-jacketing compound) causing the overcoat to pull away from the strength member and form a gap through which water may penetrate.
As such, thicker walls for an overcoat are typically extruded in multiple passes to reduce the effects of shrinkage of the overcoat material during cooling, as opposed to a single pass. Furthermore, the overcoat walls may also limit the speed at which the line can run in order to further control the cooling rate. A need exists for a method of sealing an overcoat around a strength member, such as in the central guide of a loose tube fiber optic cable, that allows for a faster line speed and/or single pass down the line, thereby improving manufacturing efficiency.